After taking on the big and small screens, comic book heroes like Spiderman and Superman may soon be appearing on an even smaller screen, your mobile phone.

After taking on the big and small screens, comic book heroes like Spiderman and Superman may soon be appearing on an even smaller screen, your mobile phone.

Suit-clad businessmen reading comic books are a common sight on Japanese trains, but they could soon be poring over their phones with publishers increasingly digitalising their comics to cash in on the country's mobile-savvy consumers.

The July 11 launch of Apple Inc's iPhone could also spur the growth of the mobile comic market as the device's touch-screen would make it easier and more appealing to read comics on handsets, analysts say.

As the number of mobile phone subscribers approaches 108 million, or 85 percent of Japan's population, carriers are moving away from voice services, beefing up content services and data transmission to increase revenues.

E-mailing, music-downloads and Internet surfing are already popular, and analysts expect comics to be the next big thing with the number of titles for mobile use soaring recently.

Comics led the size of the mobile publication market to double in the last business year to 22 billion yen ($204 million), according to Internet and media research firm Impress R&D. The size is almost three times bigger than the e-publication market for PCs.

"Until now, users had been extensively using mobile phones for emails," said Shinko Securities analyst Tomohiko Okugawa said. "Now that's shifting to games and comics ... this is the area it's going to be very interesting."

"We cannot be ahead of competition just by prices, features and sounds like we used to, and now we have to improve contents and user-friendliness to position ourselves apart from the rivals," said Toshitake Amamiya, general manager of KDDI's content and media division.

"The importance of contents has been growing ... It is crucial to pursue what we can do in this market where each adult always carries around a mobile phone and uses it as a life tool."

Nikko Citigroup analyst Hiroshi Yamashina said the bigger, better screens of new cell phones will help make mobile comics more popular.

Carriers have been releasing handsets in collaboration with popular TV brands, with some of them boasting 3.3-inch screens. Yamashina said the launch of Apple Inc's iPhone would also push up popularity of mobile comics as it can revive the sense of turning pages on its touch-screen.